Method of producing group iv-a metals



United States Patent METHOD OF PRODUCING GROUP IV-A METALS No Drawing. Application January 31, 1955 Serial No. 485,287

6 Claims. (Cl. 75-345 Thisinvention relates to the preparation of metals from group IV-A of the periodic table and more particularly to novel methods for effecting their preparation. More specifically, it relates to titanium or zirconium metal production by reducing a halide of such metal, especially a chloride, with a reducing metal, such as magnesium, and under conditions which will prevent objectionable iron contamination of the metal product.

Titanium and zirconium metals can be prepared by reducing their halides, e. g., titanium tetrachloride or zirconium tetrachloride, with a molten reducing metal, such as magnesium. Among known reduction procedures therefor, those disclosed in U. S. Patent Nos. 2,205,854, 2,564,337, 2,647,826, 2,663,634, 2,567,838 can be mentioned. The goal in such preparation is to obtain a product having the greatest possible purity, and many precautions and strict manipulative procedures have been proposed and are resorted to in attempts at attaining that goal.

The production'of a low iron contaminated metal from such reduction procedures is highly desirable because the purity of the sponge titanium or zirconium metal reaction product is animportant factor in its ultimate usefulness. In titanium metal, iron is considered to be a strong betaformer, but the betaphase is not very stable in the contamination range of less than .05% iron. Iron present in titanium metal is detrimental because difiiculty is encountered in producing all alpha alloys and the stability of the beta phase is low injmixed or all beta alloys. The reactor apparatus and equipment used in such production is constructed of iron which often enters as an objectionable impurity into the metal product due to inadvertent corrosion and attack of the equipment; To obviate this, recourse to expensive reaction vessel liners, made up'of a refractory metal such as molybdenum have been proposed. These liners shield the ironvessel from the reactants and reaction products and prevent the titanium metal product from reacting directly with the iron reaction vessel. Other typesof liners have been proposed, such as a removable low carbon steel sheeting material which is shaped to conform to the internal surfaces of the reaction vessel and is provided with a tapping outlet through which metal halide reaction by-product can be removed during the reduction.

In utilizing these liner elements, it has been customary that their surfacesbe carefully cleaned and polished before use to remove all oxide scale or other surface coating therefrom with a view to avoiding iron or other metal contamination of the end product. Thus, in the Bureau of Mines Publication, IC 7381, November 1946,

the teaching appears that prior to the reduction, the

inside surfaces of the reactor are carefully cleaned by pickling in dilute HCl, scraping, and a final polishing with emery. Again, in the Bureaus publication, R145 19, August 1949, it is taught that in setting up the equipment Jfor'the reduetion, the first step is to thoroughly clean and polish "the internal 'surfacesof'the-reactor pot with :1

a rotating sand disc to remove scale and then the under- 2,860,966 Patented Nov. 18, 1958 ICC surfaces of the reactor lid are dried prior to polishing with a rotary iron brush. Obviously, prior workershave been convinced that iron oxide scale presence on equipment employed in the reduction operation detrimentally affected the quality of the titaniu'rnmetal product derived in the reduction. v

I have found, contrary to previous practice: and under standings, that cleaning and polishing the internal surfaces of an iron containing reaction vessel orthe protectiveliner element utilized therein is disadvantageous in the metal halide reduction operations referred to, and that rather than minimizing or preventing iron contamination of the metal product such pretreatment promotes and induces undesired iron contamination. My further discovery is that, quite unexpectedly, said contamination can be effectively prevented or minimized by' carrying out the reduction operation within a reaction vessel or protective liner,the surfaces of which are coated with a relatively thin, protective layer of iron oxide.

It is among the objects of this invention, therefore, to provide an improved method for producing a relatively pureform of group IV-A metal, especially titanium or zirconium, in which objectionable iron contamination of the product is eifectively avoided; to provide novel meth ods and means for obtaining such productland without recourse to the disadvantageous, expensive, and timeconsuming reactor surfeice polishing and descaling operations considered essential heretofore; and to provide a novel reduction process from which increased yields of realtively pure titanium or zirconium metal can be readily obtained. Other objects and advantages of the invention will be evident from the ensuing description.

These and other objects can be attained in this invention which comprises preparing ametal from group IV-A of the periodic table by reducing a. halide of said metal under an elevated temperature within a closed reaction vessel the internal surfaces of which are coated with a protective layer ofiron oxide. a

The invention will be described in its application to' one preferred adaptation involving the preparation of titanium metal by reducing titanium tetrachloride with a pool of molten magnesium in a closed reactor maintained at temperatures ranging from about 7501100 C. In such operation iron contamination can arise from two sources. Thus, when reaction conditions vary beyond the close control required in the process and reaction temperatures above a limit of say 950 C; prevail, contact between the titanium metal product and the iron induces objectionable alloying at such point of contact.

Both iron and titanium are soluble in liquid magnesium, with iron being about 13 times as soluble as titanium at 900 C. The iron over and above the amount that can precipitate the titanium in solution combines with the titanium sponge and diffuses into the titanium surface. Consequently, contamination can also arise from solution of the iron in the container by the liquid magnesium metal and reaction of the dissolved iron with the titanium product. The reaction of dissolved iron with the titanium appears to be continuous with the iron being removed from the reaction container and transferredto the titanium metal. It is to the prevention of this latter type of contamination that the present invention is principally directed.

In accordance with this invention and in opposition to prior procedures which utilize oxide-free iron in contact withthe liquid magnesium, I employ an oxide coated reaction vessel or container, especially one having a mill scale type of coating over its internal surfaces. Such types of vessels and containers have been highly efficacious in preventing undesired iron contamination. For example, I utilize within the reactor a suitableopenended removable liner or casing element made up of hot- IQILQQJQWWbQn. t el. a d element'beins shaped to haiatefior configurati n o the r act r and, ha in ne e sary inlet and outlet means for introducing reactants and withdrawing reaction by-products. Preferably, this secondary reactionyessel is made up of oxide-coated sheet steelmaterial having'a thickness of, say, f rom .01 to .4 inch and since titanium or Zirconium react with. carbon at relatively high temperatures, a carbon content of only .02 to 3%. Its seam or seams can be welded or otherwise suitably secured by means of similar light material which allows the liner to be readily stripped from the sponge metal reaction product after Withdrawal from the reactor. The upper limits of the liner within the reactor canjterminateshort of the limits of the vertical walls of the reactor and at apeint above the'level of the reactant nesium, .is;then1 introduced therein. The reactor is then covered; in secured, air-tight relationship, and an argon or other suitable rare inert gas atmosphere is provided and. maintainedhtherein from a source of supply and until pressureconditions within the'reactor are maintained in suitable, adjusted extent. Heat is then applied to the reactorbysuitable furnacing or electricalheating means torm'elt, themagnesium and maintain the reactor at temperatures'ranging from about 750-4100" C. Upon reduction ofthe magnesium to molten state, liquid titanium tetrachloride is;introduced at a controlled rate into the reactor, is'inirnediatelyvaporized therein and reacts with the magnesium to formfree titanium metal sponge. This secures itself'to, bridges acrossith'e liner and builds up therein, for. subsequent removal withithe liner for recovery. The released chlorine forms magnesium chloride with the reducing metal. This settles to 'the bottom of the reactor and flows downwardly into its bottom outlet for-withdrawal, as "desired fromthe' system. Upon completion of the desired reaction, the liner or casing element together with its contained titanium metal reaction product is subjected to conventional purification treatment. The purified sponge metal is then recovered from-the casing'by stripping the latter therefrom, and

can -be for-medinto ingots or briquettes 'and fabricated into' the desired metal or alloy product.

Toma clearer understanding of the invention, the followingillustrative example is given which is not to be construed as limiting the invention:

' Example The reduction apparatus used .comprised an externallyheated, cylindrical, nickel-bearing steel reaction vessel 'havinga 12" internal diameter and a height of 20".

Within-the reaction chamber of this vessel a removable, open-ended hot-rolled mill scale oxide coated low carbon 1 (.t)f5%-) sheet steel liner having a .06" thickness, a diam- 31 1 Off-11%, and a height of 19 .Was fitted. This liner shaped to conform to-the internal configuration of. the

' reaction'vessel and was equipped, as was the vessel, with abottom d1scharge spout arranged in coaxial relationship with abottominlet into the vessel. The reactor. wasmaintained at a temperature of 850 C. by means of an exterr al-heater after all reactor inlets were sealed against the atmosphere, and an argon atmosphere was maintained therein; lbs. 'ofgsolid magnesium'metalg'previously charged into' the retaining, protective liner, were then melted" Liquid titanium tetrachloride was then introduced into, the reactorvia an inlet in its "upper portion-and onto the surface of the molten magnesium. Such introduction was effected at a rate of about lbs. per hour.

form a liquid halide as a by-product in the reduction The titanium tetrachloride liquid immediately vaporizedyt e t teined heat o th ea tor nq'wasthersaees. reduced by the molten magnesium. Magnesium chloride formed in the process settled to the reactor bottom to' How through its descending-coaxial disposed discharg spout and into a sealed cup disposed over the discharge outlet for said spout. Due to the cooler state of said outlet, the chloride cooled and solidified within the spout. and its associated sealed cup to effectively prevent fu ther by-product chloride discharge from the reactor. T tanium metal sponge formed Withinthe linerbridged across and built up therein between its Walls. Magnesium chloride by-product was drained from the reactor by re melting the frozen mass in the seal cup to allow the molten salt to flow'therefrom and materially reduce 't tanium metal sponge contamination. When essentiallyall of the reducing metal had been consumed by the reaction and magnesium chloride tapped off, the equipmentwas cooled and the liner, together with its contained titanium metal sponge, was lifted out of the reactoran conveyed to 'a final purification stage of the sys tem=' which vacuum distillation equipment was effected at about 975'-1000 C. In this latter operation any remainin magnesium chloride or other contaminants in the'sponge: were removed. Upon cooling the purified charge, the liner was easily peeled away from the titanium sponge, the. latter being then ready for melting, casting or. otherco ventional forms of treatment or fabrication.

An identical operation to the above was carried out ex. cept that the steel liner used consisted of one accordin' with prior practice, i. e., previous to use it had-been pickled, cleaned and dried, and then buffed and polishe. with a wire wheel until bright and oxide free. 1

Samples of each of these runs were taken and analyze for iron contamination with the following results: the:t tanium resulting from use of the hot rolled oxide steel liner contained 0.23% iron, while the titanium from the pickled oxide free steel liner analyzed 0.36%v iron. The latter is unacceptable as highest specification grade com mercial titanium metal whereas the product fromthe oxide coated liner operation was Wholly suitable for andmet. highest specification grade requirements. 1 i i Although described as applied to certain specificand preferred embodiments, the invention is obviously not re. stricted thereto. While magnesium comprises azpreferred: type of reducing metal, other metal reducing agents. ca also be used. Generally, use is contemplated or any re' ducing metal which is more electropositive than the pre ferred titanium or zirconium metal under production. In addition to magnesium alkali and alkaline earth metals, including calcium, barium, strontium, sodium, potassium or lithium, can be employed. These are moltenat 750? C..or higher, have relatively low specific gravities, and

action, to enable ready separation and removal. ofby product halide from the metal. j

As already indicated, the two. metals preferred for pro.-. duction in this invention comprise titanium and zirconium. Generally, however, any group IV-A metal may be prepared hereunder, including titanium-zirconium, hafnium, etc. i In such production, any 'of the halide'sjofj. said metals may be employed, particularly those in which the halogencomponent has an atomic number greater. than 9, i. e., chlorine, bromine, or iodine; The chlorides of said metals, especially TiCl; and ZrCl are particu larly useful herein and are therefore preferred for em ployrnent; The iodides and bromides of said metals. an: solids at room temperature, and while :utilizable herein are economically unattractive for use because of their rela tively'high cost. i

The only major difference between thepreferred ti tanium and zirconium producing processes is that when. employing the tetrachlorides at atmospheric pressures; zirconium tetrachloride is a solid which'sublimes atabout' 300 C., while titanium tetrachloride is a 'liquidat'abo as a liquid pool within the liner.

tween -.-30 C. and 136.4 C. Since it is easier to admit gaseous zirconium chloride to the reaction chamber than the same compound in the solid state, one may readily elect to heat the reactant material prior to use in order to admit it to the system in a fluid or gaseous state. Thus, the chosen method of addition of the zirconium chloride may be different. Aside from this,.these reactants may be added in any desired form,.e. g., as solids, liquids, or vapors. If added as liquids or solids, they volatilize upon introduction into the heated reactor.

In my invention, magnesium is, as noted, the preferred reducing agent. During the reduction reaction and at least in the initial stages thereof, the magnesium exists The initial charge of magnesium can be added as solid ingots, bars, chips and melted in the liner, or it may be .added in liquid state to the liner before initiating the reaction. Obviously, additional amounts of magnesium can be added during the reaction, either in the solid or the liquid state.

During the reduction the rate of reaction and the pressure prevailing within the reactor can be readily controlled by recourse to a neutral or inert atmosphere. While argon comprises a preferred form of protective gas, other inert gaseous elements of the group O of the Periodic System, such as helium or neon, or mixtures thereof, can he used. In employing the argon, a substantial partial pressure of such gas is maintained within the reactor during the reaction. This is adjusted to 760 mm. or higher during the tapping operation to avoid air infiux and while the contents of the vessel are at or above the melting temperature of the metal halide reaction product. Alternatively, atmospheric or pressures above atmospheric (say, from 1-3 atmospheres or higher) can be employed, if desired.

The term oxide scale as used herein refers generally to the chemical compounds of iron and oxygen formed on the surface of steel by exposure to air while the metal is at an elevated temperature. Specifically, it comprises the oxidized surface of the steel produced during heating or working and during hot working. Hence, the oxide produced on a steel surface in hot rolling processes is known as mill scale. Chemical compounds thus formed comprise the various iron oxides, FeO, Fe O and Fe O The mechanism whereby mill scale forms is generally considered to be of a dynamic nature whereby alternate formation and reduction of the higher oxides of iron occur. Fe O is formed first and then reduced successively to Fe O and FeO by the availability of the iron during progress from the outer surface towards the iron center. The layer next to the steel, FeO, constitutes about 85% of the scale thickness; Fe O the intermediate layer, about l-15%; and Fe O the outer layer, about /-2%. This scale exists on the hot rolled sheet steel product as it leaves the mill.

Oxide coatings can be produced on cold-rolled or pickled metal products by surface conversion coatings, such as blue annealing, steam-bluing, air-bluing, or Barifiing treatments. While these types of oxide protective coatings are utilizable, the economics involving their use for liner purposes may not be as favorable as with hot rolled steel, because the steel base, prior to the treatment has been carried through a hot-rolling, pickling and possibly cold rolling operation.

While I prefer to employ a removable form of hotrolled sheet steel protective liner, it will be evident that the liner element can be fixed or stationary within the reactor and form a component part thereof. Also, it is obvious that the oxide coating can be suitably applied to and formed directly on the internal surfaces of a steel reactor shell should use of a liner element be dispensed with. Thus, prior to use, such surfaces can be subjected to suitable oxidation treatment under elevated temperatures, conditions which will form thereon the desired protective oxide scale coating.

I claim as'my invention: v

1. A process for preparing a metal from group. IV-A of the periodic table selected from the group consisting of titanium,.zirconium and hafnium which comprises reducing a halide of said metal selected from the group consisting of a chloride, bromide and iodide with a reducing metal selected from the group consisting'of alkali and alkaline earth metals, effecting said reduction under an elevated temperature ranging from 7501100 C. within a closed reaction vessel the internal surfaces of which vessel are coated with an adherent protective layer consisting essentially of iron oxide selected from the group consisting of FeO, F6303, Fe O and mixtures thereof, said layer constituting the only vessel contact with the reactants and reaction products during there duction, and thereafter purifying and recovering the metal product. V p

' 2. A method for producing titanium metal which comprises reducing a titanium halide selected from the group consisting of a chloride, bromide and iodide under an elevated temperature ranging from 750-1100 C. with magnesium within a closed reaction vessel the internal surfaces of which are coated with an adherent protective layer consisting essentially of iron oxide selected from the group consisting of FeO, Fe O Fe O and mixtures thereof, said layer constituting the only vessel contact with the reactants and reaction products during the reduction, and thereafter purifying and recovering the titanium metal product.

3. A method for producing zirconium metal which comprises reducing a zirconium halide selected from the group consisting of a chloride, bromide and iodide under an elevated temperature ranging from 750-1100 C. with magnesium within a closed reaction vessel the internal surfaces of which are coated with an adherent protective layer consisting essentially of iron oxide selected from the group consisting of FeO, Fe O Fe Ol. and mixtures thereof, said layer constituting the only vessel contact with the reactants and reaction products during the reduction, and thereafter purifying and recovering the zirconium metal product.

4. A process for producing titanium metal which comprises reducing at a temperature of from 750-1100 C. titanium tetrachloride with molten magnesium within a closed reaction vessel and a sheet steel liner having an adherent oxide coating for said vessel consisting essentially of iron oxide selected from the group consisting of FeO, Fe O Fe O and mixtures. thereof, said coating constituting the only vessel contact with the reactants and reaction products during the reduction, upon completion of the reduction reaction removing said liner with its contained titaniummetal product from said vessel and subjecting the same to purification treatment, and upon completion of said purification, recovering the purified titanium metal product from said liner.

5. A process for producing titanium metal comprising reducing at a temperature of from 750-1100 C. titanium tetrachloride with molten magnesium within a closed reaction vessel and a removable hot rolled mill scale oxidecoated steel liner, the mill scale oxide coating consisting essentially of iron oxide selected from the group consisting of FeO, Fe O Fe O and mixtures thereof and which constitutes the only vessel contact with the reactants and reaction products during the reduction, upon completion of the reduction reaction removing said liner and its contained titanium metal product from said vessel and subjecting said product to vacuum distillation purification treatment within said liner, and subsequent to completion of said purification stripping said liner from the purified metal to effect recovery of the latter.

6. A process for producing zirconium metal comprising reducing at a temperature of from 750-1100 C. zirconium tetrachloride with molten magnesium within a closed reaction vessel and a removable hot rolled mill scale oxide-coated steel liner, the mill scale oxide coating consisting essentially of iron oxide selected from the gro n; consisting of FeO, Fe 05,"" Fe' Q and mixtn'res thereof and-"which constitutes theionly' vessel contact with the-reactants and"reactipn products {:lflrihgth reduction,

upon completion of the reduction reaction remo ving'said "linctfandit's contained z'i rconiu rn metal product froin said J yss'cl ind siibjccting'"said 'product to v ac muin distillation pu'rificatipn' tyatn entwithin saigi liner, and subseqnent f0 g mgl t ionof "said'pur'ifi cationstripping saigi line-1f from the p'urified metal-to effect irecovry ofthe latter.

I: llefe l'encesiCited in theifile .of this patent N E S "P l NTfi V,

OTHER REFERENCES Evan s; Corrosion of -Metals, .pp. 22923 1.; publ. L926 7 by litltArnold '.&.Co., London. r

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8 V Rawdon: Protective Metallic Coatings, pp. 53-54; publ "The Elctrochem. So'c.- Preprint, 78-1 I, October 7,1340, Pu im-1172.53 1 7 l 16, 1947, pp. 3 63-'364. 7 t i MetalzProgiess'jFebruary- 1949; pp. 188490. 7

Productionbin-Ductile, Titanium; by Wartma'n -et a] Bnreauof Mincs R. 1.4519, pubL- August 19491-by Bureau I upon; 7

pages 6 and 24 peptinenn however, entire report rcl ied 'ModemM etels, vol. =VIII, No. 1, Februany l 9f 2g-pfi J. of'lthc Electrochern Soc., vol.- 101, No; 10,1 October 1954,}Pag'es 507 -513. Y 

1. A PROCESS FOR PREPARING A METAL FROM GROUP IV-A OF THE PERIODIC TABLE SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM AND HAFNIUM WHICH COMPRISES REDUCING A HALIDE OF SAID METAL SELECTED FROM THE GROUP CONSISTING OF A CHLORIDE, BROMIDE AND IODIDE WITH A REDUCING METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI AND ALKALINE EARTH METALS, EFFECTING SAID REDUCTION UNDER AN ELAVATED TEMPERATURE RANGING FROM 750-1100*C. WITHIN A CLOSED REACTION VESSEL THE INTERNAL SURFACES OF WHICH VESSEL ARE COATED WITH AN ADHERENT PROTECTIVE LAYER CONSISTING ESSENTIALLY OF IRON OXIDE SELECTED FROM THE GROUP CONSISTING OF FEO, FE2O3, FE3O4, AND MIXTURES THEREOF, SAID LAYER CONSTITUTING THE ONLY VESSEL CONTACT WITH THE REACTANTS AND REACTION PRODUCTS DURING THE REDUCTION, AND THEREAFTER PURIFYING AND RECOVERING THE METAL PRODUCT. 